The present invention relates to medical linear accelerators and, more particularly, to a system and method for reducing the effects of backheating on the electron gun in a medical linear accelerator.
Radiation emitting devices are generally known and used, for instance, as radiation therapy devices for the treatment of patients. A radiation therapy device generally includes a gantry which can be swiveled around a horizontal axis of rotation in the course of a therapeutic treatment. A linear accelerator including an electron gun and a waveguide is located in the gantry for generating a high energy radiation beam for therapy. This high energy radiation beam can be an electron beam or photon (X-ray) beam. During treatment, this radiation beam is trained on one zone of a patient lying in the isocenter of the gantry rotation.
An important consideration in delivering radiation treatment is control of the radiation beam. The electron gun is subject to a phenomenon known as xe2x80x9cback heating.xe2x80x9d Backheating causes an increase in the temperature of the electron gun resulting in an increase in the barium evaporation rate (Barium is impregnated into the gun cathode tungsten matrix to enhance electron emission.). This causes a deposition of barium in cavities of the linear accelerator adjacent the electron gun. This, in turn, results in an increase in dark current, which has a deleterious effect on the control of the radiation beam. The net result is that the linear accelerator""s useful life is decreased, and therefore must be replaced sooner than would necessarily be desired.
As such, there is a need for controlling the barium evaporation rate in an electron gun. There is a still further need for a medical linear accelerator having a relatively longer useful life.
These and other problems in the prior art are overcome in large part by a system and method for control of a radiation therapy device according to the present invention.
A radiation therapy device according to an embodiment of the present invention includes a programmable power source and controller that monitor an injected current level and controls heater voltage in response thereto. The heater voltage is reduced in predetermined increments without affecting the beam profile.
A filament voltage controller according to an embodiment of the present invention includes an injector and a remotely programmable electron gun power source. A controller receives an injection trigger signal from the injector, and a measurement of the injection current. The injection current is measured during runup and when RAD ON commences, cuts back the filament voltage a predetermined amount, and measures the current again. So long as the injected current does not fall below the run up level, the heater voltage will be reduced incrementally.